493 



of the seas, wherever places so distant present 

 some analogy of temperature ? Notwithstand- 

 ing the influence, which the pressure of the air, 

 and the greater or less extinction of light, exert 

 on the vital functions of plants, it is no doubt 

 heat, unequally distributed in different seasons 

 of the year, that must be considered as the 

 most powerful stimulus of vegetation. 



The number of identical species in the two 

 continents and in the two hemispheres is far 

 less, than the assertions of the first travellers led 

 us to believe. The lofty mountains of Equinoc- 

 tial America have certainly plantains, valerians, 

 arenarias, ranunculuses, medlars, oaks, and 

 pines, which from their physiognomy we might 

 confound with those of Europe ; but they are all 

 specifically different. When nature does not 

 present the same species, she loves to repeat 

 the same genera. Neighbouring species are 

 often placed at enormous distances from each 

 other, in the low regions of the temperate zone, 

 and on the alpine heights of the equator. At 

 other times (and the Silla of Caraccas displays 

 a striking example of this phenomenon,) they 

 are not the European genera, which have sent 

 species, to people like colonists the mountains 

 of the torrid zone ; but genera of the same tribe, 

 difficult to distinguish by their appearance, 

 which take the place of each other in different 

 latitudes. 



